Alimony calculation in the United States is far less standardized than child support. While child support uses mandatory formulas in all 50 states, alimony calculation ranges from precise statutory formulas in a handful of states to broad judicial discretion in most. Understanding which approach your state uses is the essential first step in estimating your obligation or entitlement.
The AAML Benchmark Formula
The American Academy of Matrimonial Lawyers (AAML) formula is the most widely referenced benchmark for alimony estimation nationwide. It is not law in most states, but family law professionals use it as a starting point for negotiation and as a reasonableness check on proposed settlements.
The formula: Alimony = (30% × payor's gross monthly income) − (20% × recipient's gross monthly income), with the recipient's total income (salary plus alimony) capped at 40% of combined gross income.
Example: Payor earns $8,000/mo gross. Recipient earns $2,500/mo gross. AAML estimate: (30% × $8,000) − (20% × $2,500) = $2,400 − $500 = $1,900/mo. Combined cap check: ($8,000 + $2,500) × 40% = $4,200 total recipient income allowed. $2,500 + $1,900 = $4,400 — exceeds cap. So alimony is reduced to $1,700 (making recipient total = $4,200). Final: $1,700/mo.
Illinois Statutory Formula
Illinois is one of the few states with a codified alimony formula. Called "maintenance" in Illinois law, the calculation uses net income rather than gross: (33.3% × payor's monthly net income) − (25% × recipient's monthly net income), capped at 40% of combined net income.
Illinois also has a statutory duration schedule based on marriage length — the duration is calculated as a percentage of the marriage length ranging from 20% for marriages under 5 years to permanent support for marriages of 20+ years.
California Santa Clara Formula (Temporary Support)
California uses the Santa Clara formula for temporary spousal support (during divorce proceedings): (40% × higher earner's net monthly income) − (50% × lower earner's net monthly income). This formula is widely adopted across California's 58 counties for temporary orders.
Permanent spousal support in California has no formula. A judge must weigh 14 statutory factors under Cal. Fam. Code § 4320, including marital standard of living, earning capacity, age and health, domestic violence history, and each spouse's career contributions and sacrifices.
States With Judicial Discretion (Most States)
The majority of states give judges broad discretion to set alimony based on a list of statutory factors. Common factors across all states:
- Income and earning capacity of each spouse
- Length of the marriage
- Standard of living established during the marriage
- Age and physical/mental health of each spouse
- Contributions to the marriage (including homemaker contributions and supporting the other spouse's career)
- Time needed for the recipient to gain education or training for employment
- Marital fault (in states that consider it)
How Marriage Length Affects Alimony
Marriage length is the single most important factor for alimony duration in virtually every state. It also affects the amount in many states — longer marriages typically produce higher awards because the income gap has had more time to widen and the lower-earning spouse has had less opportunity to build independent career equity.
| Marriage Length | Typical Duration | Amount Impact |
|---|---|---|
| Under 5 years | 1–3 years | Lower — less career sacrifice assumed |
| 5–9 years | 2–5 years | Moderate |
| 10–14 years | 4–7 years | Moderate to significant |
| 15–19 years | 7–12 years or more | Significant |
| 20+ years | Indefinite / permanent | Highest — full standard of living restoration |
How Courts Handle Large Income Gaps
Courts in discretionary states do not mechanically apply the AAML formula. But the income gap between spouses is the central variable in every alimony analysis. A large gap (over $5,000/month) almost always results in some alimony in marriages of meaningful length. A modest gap (under $1,500/month) often produces little or no alimony, particularly in shorter marriages.
The recipient's earning capacity matters as much as current income. A spouse who voluntarily left the workforce to raise children has a gap between current income and earning capacity — and courts typically award alimony sufficient to bridge that gap during a reasonable re-entry period.
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